This invention is directed to a process for the conversion of hydroperoxides present in allyl-alkyl ether to enhance the use of such ether as a feedstock in a rhodium catalyzed hydroformylation process to produce the corresponding ether aldehyde. Such hydroperoxides are decomposed by treating the ether with metal hydride to give products which include .alpha.,.beta.-unsaturated aldehydes, which are then reduced to the corresponding alcohols.
Hydroperoxides, which may form in allyl-alkyl ether by adventitious air oxidation, decompose during hydroformylation to form .alpha.,.beta.-unsaturated aldehydes such as acrolein, among other by-products. The effect of acrolein and closely related compounds as rhodium catalyst inhibitors is known in the prior art. U.S. Pat. No. 4,148,830 issued Apr. 10, 1979, indicates, at Column 4 lines 65 et. seq., that it is highly desirable to maintain "substituted acrolein II" (i.e., ethylpropylacrolein) at low concentrations "since it has been observed that a build-up of this product tends to curtail the life of the rhodium complex catalyst."
The effect of the presence of acrolein in allyl-alkyl ether used as a feedstock in a rhodium catalyzed hydroformylation reaction to produce the corresponding ether aldehyde is seen in Example 1 in Table I below. It is postulated that this catalyst induction period occurs because of the competition for the rhodium catalyst between the hydroformylation reaction and the reaction to reduce acrolein to propanol and/or propionaldehyde. Such a catalyst induction period is effectively eliminated by removing hydroperoxides and acrolein from the allyl-alkyl ether. See Examples 2-4, infra, and Table I below.
According to J. A. Riddick and W. B. Bunger, "Techniques of Chemistry" Vol. 2, p. 690 "Organic Solvents" Wiley-Interscience (1970), solutions of phenothiazine, iron (II) sulfate, tin (II) chloride, copper-zinc couple, sodium bisulfite, alkali metal hydroxides, cerium (III) hydroxide and lead (IV) oxide have all been found to destroy peroxides in ethers. However, none of the above reagents is known to be effective in removing or reducing acrolein as well.
Riddick and Bunger, supra at p. 691 also discloses that passing impure ether through an activated aluminum oxide column will reduce aldehyde content as well as remove peroxide. However, research has revealed that only a relatively small quantity of acrolein is adsorbed on the alumina and retained (See Example 2 and Table I below). Thus alumina cannot effectively be used for the purification of large quantities of allyl-alkyl ether without adding complicated and expensive processing steps to avoid eventual acrolein breakthrough with the allyl-alkyl ether effluent.
M. Ross Johnson and Bruce Rickborn "Sodium Borohydride Reduction of Conjugated Aldehydes and Ketones", J. Org. Chem. Vol. 35, p. 1041 (1970) show the use of aqueous alkali metal borohydrides as reducing agents for aldehydes, including the reduction of acrolein to allyl alcohol and propanol. Similarly, British Pat. No. 981,965 describes the use of alkali metal borohydride to reduce the residual aldehyde content in Oxo alcohol after hydroformylation. However, neither reference discloses the use of alkali metal borohydrides to reduce hydroperoxides and simultaneously to reduce the acrolein formed during the reduction of the hydroperoxides in allyl-alkyl ethers.
U.S. Pat. No. 3,003,002 discloses a means of removing peroxides from diethyl ether by contact with a strong base anion exchange resin in its hydroxyl form. However, this treatment will only remove peroxide and will not remove aldehydes, as such bases will not react with .alpha.,.beta.-unsaturated aldehydes in such manner as to tie them up.
British Pat. No. 876,034 and U.S. Pat. No. 4,107,099 both disclose the manufacture of borohydride exchange resins. In addition, U.S. Pat. No. 4,107,099 contains several examples of the use of such resins. Example 12 discloses the reduction of crotonaldehyde, as an undesirable impurity in synthetic ethanol, in concentrations of 20 to 500 ppm. Example 15 discloses a qualitative reduction of peroxides in tetrahydrofuran, such reduction being monitored by qualitative analysis employing an iodide test in which an intense red-brown color will indicate the presence of substantial peroxide.
It has now been unexpectedly found that treatment with metal hydrides will convert hydroperoxides in allyl-alkyl ethers to acrolein and other decomposition products not harmful to the hydroformylation reaction, and will then reduce the acrolein to propanol and/or propionaldehyde without reducing the olefinic double bond in the allyl-alkyl ether. The novel metal hydride treatment will eliminate the catalyst induction period present in the hydroformylation reaction when partially oxidized allyl-alkyl ether is employed as a feedstock for conversion to its corresponding ether aldehyde. This is because the treatment will free the rhodium catalyst for the hydroformylation reaction, eliminating the competing acrolein to propanol and/or propionaldehyde reaction. See Table I below.